Due to their compact size, high efficiency and long lifetimes, light emitting diodes (LEDs) have replaced incandescent light sources in a variety of power signaling applications which require high intensity, colored light. Although light emitted by LEDs is inherently dispersed over a wide angle, automotive tail lamps, traffic signal lights, moving message displays and other power signaling applications require that light be confined within a narrow viewing angle. In fact, the Society of Automotive Engineers (SAE) specifies luminous intensity versus viewing angle relative to an optical axis in the horizontal and vertical planes for automotive tail lamps. Various systems have been used to efficiently redirect the light from LEDs in order to achieve a high luminous intensity within a desired viewing angle.
In the Ford Motor Company's model Taurus SHO center stop lamp, a lens is positioned in front of an LED. The lens, in conjunction with a metallized parabolic surface placed behind the lens, redirects light emitted by the LED into a narrow viewing angle. Although light is efficiently redirected, the metallized surface increases manufacturing costs for this type of system.
A prior art collimator for an LED array is taught by Nichols et al. in U.S. Pat. No. 4,767,172. Nichols et al. utilizes a lens in front of an LED in combination with a transparent integral collector to collimate light parallel to an optical axis for projection into a light pipe or optical waveguide. Although this type of collimator efficiently redirects light, and may have low manufacturing cost, the light is limited to on-axis viewing, making this type of system unsuitable for power signaling applications.